In the field of weight lifting, dumbbells and barbells comprise an elongated handle or bar that is loaded at either end with a plurality of weight plates. Assuming the weight plates are of the same weight relative to one another, the exercise weight provided by the dumbbell or barbell is adjusted by changing the number of weight plates installed on each end of the bar. The major difference between a dumbbell and barbell is the length of the bar that carries the weight plates. A dumbbell has a relatively short handle or bar that can be gripped by just one hand of the user. A barbell has a much longer bar that can be gripped by both hands of the user with the user's hands being spread apart along the length of the bar at approximately the width of the user's shoulders.
Both barbells and dumbbells are often referred to as free weights. Free weights are not built into nor have their motion determined or limited by some type of machine that carries the weights. Instead, a user can grip and use a free weight in three dimensional space without being constrained in having to move the weight along a predetermined two dimensional path as in a typical exercise machine. Thus, in using free weights, the weight lifter must not only lift the free weight but stabilize the motion of the free weight in all three planes of motion, just as an athlete must use his body and strength in three dimensions on a playing field. While exercise machines have been developed and are useful for isolating and building strength in various muscles, many people consider free weights to be superior to such machines due to the three dimensional stability the user must impart to a free weight while lifting the free weight.
One problem with the use of free weights is how the exercise weight carried on the bar is adjusted. This is typically done simply by adjusting the number or the size of the weight plates carried on either end of the bar. As the user goes from one exercise to another, he or she will usually change the exercise weight for each exercise, i.e. the user probably wants more weight on the bar during a front squat than when doing a bench press. So, the user is continually changing the weight plates on the ends of the bar between exercises to adjust the weight. This can be a time consuming and frustrating task.
Another more serious problem with free weights is their potential to injure the user. Since the exercise weight provided by a free weight is directly loaded onto the bar in the form of the weight plates carried by the bar, there is no way for a user to get out of the way of this weight should the user become fatigued and drop the bar. The risk of injury can be lessened if the user employs a second person as a spotter, i.e. a person who stands by while the user is exercising and helps catch and support the bar if the user can no longer lift the bar or drops the bar. The risk of injury can also be lessened if the user properly sets safety bars on a power cage in which the user is lifting so that the safety bars would catch the bar if the user should drop it.
Unfortunately, however, a second person may not be available to spot the weight lifter as he or she is exercising. In addition, many weight lifters, particularly relatively inexperienced lifters, either do not use safety bars or set the safety bars too low. In these cases, if the user should drop a heavily loaded barbell onto his or her shoulders or be unable to stop or reverse the downward motion of a barbell when doing a front squat, serious injury to the user's neck or spinal cord may occur. Obviously, this is a disadvantage to the use of free weights. Any device that would permit free weight lifting to take place while minimizing the chances of injury would be an improvement in the art.